The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Gears can be hardened by an induction heat treatment to improve wear resistance. In one type of gear, the inner surface of the gear includes a plurality of splines. The splines do not cover the entire circumference of the inner surface. Instead, the inner surface includes several webs, where a series of splines are located between each web. The webs are an area of decreased wall thickness along the inner surface of the gear. It is typically desirable to heat treat only the splines, as the webs have a reduced wall thickness that is susceptible to melting or cracking.
In one approach, induction heat treatment is used to only harden the splines. However, it is not possible to only heat treat the splines with the current induction coil and process design technology. A non-rotational induction heat treatment technique is employed, where the gear is oriented in a particular position and all of the splines are concurrently heated by a coil placed within the inner surface of the gear. However, this non-rotational approach results in a non-uniform and unsymmetrical heat treat pattern, and also tends to overheat the webs, which leads to melting and cracking of the webs. As a result, several splines between each web will remain untreated in an effort to avoid overheating the web. This results in gears that do not meet heat treatment specifications. The current approach of orienting the spline with respect to the inductor coil requires special handling issues and adds to the cost of the product. Moreover, the current induction hardening process also produces very deep hardening, or case, along the outer surface of the gear. Thus, the current approach of induction hardening can produce that have built in stresses, which may lead to premature mechanical failure of the gears. As a result, there is a need in the art for a robust induction hardening process for a gear that heats the splines uniformly without overheating the webs.